But if he is actually done with UFC, I don't think he should retire and I expect him to appear somewhere else like Strikeforce or Japan.

Yeah, and plus it's not lost to some scrub. Shogun is the real deal, one of the pound for pound best in the business. No shame in that, but it's clear he's lot a few steps. So maybe retirement should be his option, I'm sure he's made a killing from his career (including endorsements).